11-(4-[2-(2-Hydroxyethoxy)ethyl]-1-piperazinyl]dibenzo[b,f]-1,4-thiazepine is a well established drug substance known under the INN name quetiapine. It is used as its hemifumarate salt having the structure or formula (1)

Quetiapine hemifumarate is a psychoactive organic compound that is an antagonist for multiple neurotransmitter receptors in the brain. It is used as an antipsychotic or neuroleptic. Quetiapine hemifumarate, as well as its synthesis, is described, for example, in the European Patent EP 0 240 228 B1. In EP 0 240 228 B1, as well as WO 01/55125, ethanol is used as the solvent component in the crystallization process of quetiapine hemifumarate.
WO 03/080065 relates to new polymorphs of quetiapine hemifumarate and their methods of preparation. It also relates to new methods of preparing the known form of quetiapine hemifumarate and it further provides post-treatment methods, like post-suspension and post-crystallization, for crystalline forms of quetiapine hemifumarate. In said post-crystallization method the crystallization solvent can be selected from lower alkanols, cyclic ethers, ethyl acetate and water.
U.S. Pat. No. 6,372,734 describes the preparation of crystalline quetiapine by crystallizing a quetiapine from a non-aromatic solvent such as ethyl acetate, isobutyl acetate, methyl iso-butylketone or methyl tert-butyl ether, preferably in the absence of water. It further describes how the crystalline quetiapine can then be treated with fumaric acid in a solvent such as an alcohol to obtain the hemifumarate salt.
WO 2004/076431 describes the synthesis of quetiapine and it further describes how the product is converted to the hemifumarate salt which can then be re-crystallized from a solvent that is a lower alkanol, preferably ethanol, or a mixture of water and a dipolar aprotic solvent, preferably dimethyl formamide.